Biosynthesis of Zinc Oxide Nanoparticles using Fermented Table Olive Extract: A Novel and Green Approach with Potential Applications

This research aimed to investigate a biological method that is both new and effective for the synthesis of zinc oxide nanoparticles (ZnO-NPs) using extract from fermented table olives (FTO), with the goal of reducing the environmental impact of the process. In this study, we utilized the Gas chromatography–mass spectrometry (GC–MS) technique for the identification of phenolic compounds in FTO extract. The characteristics of the nanoparticles were identified using various analytical techniques, including dynamic light scattering (DLS), zeta potential, ultraviolet–visible (UV–Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM) for both the cell biomass precipitate (P) and supernatant (S) nanoparticles. Phenolic compounds, which are considered an important group of known compounds in FTO extract, were also present in the volatile profile. Optimization of synthesis was performed using zinc sulfate heptahydrate (ZnSO 4 .7H 2 O) at pH 12 and a 2:1 ratio of precursor to culture medium with FTO extract overnight at 37 °C. The particle size of ZnO-NPs ranged from 9 to 100 nm for ZnO-NPs-P and 300–500 nm for ZnO-NPs-S. The UV–Vis spectra showed typical absorption peaks between 300 and 400 nm, and the ZnO-NPs chemical bond was confirmed by FTIR analysis. XRD results revealed the formation of a hexagonal wurtzite structure with a crystallite size of 22.05 nm for ZnO-Np-P and the supernatant nanoparticles were non-crystalline and amorphous. FE-SEM and TEM analyses showed that the nanoparticles were spherical, and EDX analysis confirmed relatively good purity for the synthesized nanoparticles. The lattice parameter values were consistent with the standard values for ZnO-Np-P, and the mesoporous structure. The antimicrobial properties of the synthesized ZnO-NPs were evaluated against both gram-positive and gram-negative bacterial strains as well as fungi. ZnO-NPs-P demonstrated the highest bactericidal activity against Escherichia coli (16 μg/mL) and Staphylococcus aureus (64 μg/mL), while the synthesized nanoparticles exhibited a potent antifungal effect at a concentration of 64 μg/mL. The highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activities at 400 μg/mL were noted as 61.86% and 65.33% for ZnO-NPs-S and ZnO-NPs-P, respectively. The results of this study ind